Expand.
Answer: We expand the parentheses using the distributive property : $ A(B+C+D)= A\cdot B+ A\cdot C+ A\cdot D$ We can also think about the problem using an area model: $a^2$ $-10a$ $25$ $-3a$ Here's how the solution goes, algebraically: $\begin{aligned} &\phantom{=}{-3a}(a^2-10a+25) \\\\ &={-3a}(a^2)+({-3a})(-10a)+({-3a})(25) \\\\ &=-3a^3+30a^2-75a \end{aligned}$ Here's how the solution looks in terms of the area model: $-3a^3$ $30a^2$ $-75a$ $a^2$ $-10a$ $25$ $-3a$ In conclusion, $ -3a(a^2-10a+25)=-3a^3+30a^2-75a$